Energy-efficient and high-intensity light sources such as LEDs (light emitting diode) or lasers, usually in the form of laser diodes, are increasingly being used in modern lighting devices. In contrast to incandescent bulbs, which are thermal emitters, those light sources emit light in a narrowly delimited spectral range such that their light is almost monochromatic or exactly monochromatic. One possibility for opening up further spectral ranges consists of light conversion, for example, wherein phosphors are irradiated by LEDs and/or laser diodes and in turn emit light having a different wavelength. In the so-called “remote phosphor” applications, for example, a layer comprising phosphor situated at a distance from a light source is usually illuminated by LEDs or laser diodes and in turn emits light having a different color, i.e., a different wavelength. Applications are also known, however, wherein the layer comprising the phosphor is arranged directly on the light source. By way of example, those techniques can be used to convert light from blue LEDs into white light by admixing yellow light generated by the excitation of a phosphor-containing layer. The layer can be, for example, in the form of a solid body, for example, in the form of a lamina.
In the abovementioned applications, the phosphors are usually excited to emission by LEDs and/or laser diodes having high light powers. Thermal losses that arise in the process have to be dissipated, for example, via the carrier to avoid overheating and thus thermally governed changes in the optical properties or even the destruction of the phosphor.
The phosphors, usually present in pulverulent form, without an additional use of binders, for example, silicones, do not form mechanically stable layers, i.e., abrasion- and/or stretch-resistant layers. However, binders are also generally used to unite the phosphor particles into one phase, which can then be applied to corresponding surfaces. When binders are used for layer stabilization, however, the binders themselves can interact with the phosphors and thus adversely influence their optical and thermal properties, and their lifetime. Furthermore, thermal conductivity of the binders is often a limiting variable in the dissipation of heat that arises in the conversion element.
Conversion elements formed from a ceramic comprising the phosphor or from a crystal comprising the phosphor are known as alternatives. More particularly, the phosphor can form the ceramic or the crystal. Such conversion elements can be fixedly adhesively bonded to heat sinks so that the heat arising therein can be dissipated. In that case, a limiting variable for the heat dissipation is the thermal conductivity of the adhesive used. Therefore, the conversion elements can also be arranged directly, in particular without adhesive therebetween, on the light emitting component, for example, the LED chip. Furthermore, it is beneficial to good heat dissipation if the conversion elements are made particularly thin.
The phosphor is embedded in the ceramic or incorporated in the crystal structure and in various examples can be a phosphor mixture comprising a mixture of different phosphors as a result of which, for example, light combining a plurality of different colors can be generated. Suitable phosphors are known.
It is known, for the purpose of increasing efficiency of a light emitting assembly comprising a light emitting component and a conversion element, and/or for the purpose of increasing a luminance of light generated by the light emitting assembly, to embed the conversion element into silicone such that side walls of the conversion element running, for example, substantially parallel to a main emission direction of the emitted light are in physical contact with the silicone, and sides of the conversion element running perpendicularly to the main emission direction are substantially free of silicone. By way of example, the conversion element can be encapsulated with the silicone by molding. Titanium oxide, for example, which reflects the light, can be embedded into the silicone. The silicone is relatively sensitive and can easily be damaged and is therefore regularly made particularly large and/or thick, and so the size of the conversion element comprising the silicone significantly increases, for example, doubles, compared to the same conversion element without the silicone.